Effects of Dissolved Silver and Silver Nanoparticle on Soil Microorganisms

Silver nanoparticles (AgNPs) are the most commonly used man-made nanomaterial in consumer products.
They are merged into a vast collection of products due to their particular broad-spectrum anti-microbial action. On the
other hand, their anti-bacterial properties may pose a significant environmental risk. This study was undertaken to
assess whether the risk that AgNPs and dissolved Ag pose to soil microorganisms gained from nano- or dissolved-silver
forms. The antimicrobial effect of green manufactured AgNPs (46.2±23.2 nm) and Ag+ (as AgNO3) on soil microbes
were studied using disc diffusion assay. Soil microbial growth was assessed by the measurement of inhibitory zone area
(mm2) as a function of different AgNPs and AgNO3 concentrations, 0.00, 250, 500, 1000 and 2000 mgl-1. The results of
antimicrobial effect of AgNPs showed 10 fold of magnitude comparing with Ag+ at lower concentrations (250 mgl-1).
The theoretical predicted unity of inhibition zone ratio for AgNPs/Ag ions implies that AgNPs equates to about 5 times
antimicrobial effects of Ag+. Although the current results confirm that Ag antimicrobial effect is a nano-specific effect,
different bacteria isolated from different soils should be used to explore their physico-chemical properties in mitigating
AgNPs toxicity effects.